KR102237271B1 - Water vapor permeable filtration material - Google Patents

Abstract

In the present invention, a hydrophobic layer having a hydrophobicity and a hydrophilic layer having a hydrophilicity are laminated, and one of the hydrophobic layer or the hydrophilic layer is composed of a PTFE porous membrane formed using PTFE, and any of the hydrophobic layer or the hydrophilic layer The other side is composed of a breathable sheet having breathability.

Description

Water vapor permeable filter material {WATER VAPOR PERMEABLE FILTRATION MATERIAL}

The present invention relates to a filter medium having moisture permeability, and in particular, to one formed using a porous PTFE membrane.

[Cross reference of related applications]

This application claims the priority of Japanese Patent Application No. 2013-272760, and is incorporated in the description of this specification by reference.

Conventionally, two gases having different humidity are disposed adjacent to each other through a filter medium (permeable filter medium) having moisture permeability, so that moisture (water vapor) is transmitted from the gas on the high humidity side to the gas on the lower humidity side through the moisture permeable filter medium. A method of moving and adjusting the humidity of at least one of both gases is known. For example, a method of using a member configured by accommodating an adsorbent in a bag body formed using a moisture permeable filter medium is known (see Patent Document 1).

Since water vapor is adsorbed by the adsorbent in the air inside such a member, the humidity is lower than that of the air outside the bag body. Thereby, the water vapor of the outside air permeates the moisture permeable filter medium, penetrates into the inside of the bag body, and is adsorbed by the adsorbent. That is, by arranging such a member in a predetermined space, it becomes possible to adjust (humidify) the humidity of the air in such a space (air outside the pocket body).

As the moisture-permeable filter medium as described above, it is necessary to allow water vapor to permeate, and to properly divide adjacent spaces through the moisture-permeable filter material. As a material constituting such a moisture permeable filter medium, a porous polytetrafluoroethylene membrane (hereinafter, also referred to as a porous PTFE membrane) is used. It is known that such a porous PTFE membrane has good moisture permeability. For this reason, two gases with different humidity are placed adjacent to each other through the PTFE porous membrane, and while distinguishing these two gases, water vapor moves from the gas on the high humidity side to the gas on the low humidity side (transfers through the moisture permeable filter medium). ) It becomes possible.

By the way, since the above-described porous PTFE membrane is relatively thin and has no stiffness, handling is poor when only the PTFE porous membrane is used as a moisture permeable filter material. For this reason, by laminating an air permeable sheet of a certain thickness on a PTFE porous membrane, a moisture permeable filter medium having good handling properties (stiffness) has been provided.

However, since the breathable sheet is laminated on the porous PTFE membrane, the moisture permeable filter medium is thicker than that of the porous PTFE membrane alone. Here, since the moisture permeability (mobility of water vapor from one side to the other side) of the moisture permeable filter medium is inversely proportional to the thickness of the filter medium, such a moisture permeable filter medium has lower moisture permeability than the PTFE porous membrane alone. For this reason, in such a moisture permeable filter medium, water vapor cannot be effectively transmitted from one side to the other side.

Japanese Patent Application Laid-Open No. Hei 11-57377

Accordingly, an object of the present invention is to provide a moisture-permeable filter material in which a breathable sheet is laminated on a porous PTFE membrane, and a moisture-permeable filter material in which the moisture permeability of the PTFE porous membrane itself is suppressed from deteriorating.

The moisture-permeable filter material according to the present invention is a moisture-permeable filter material formed in a sheet shape and configured to allow water vapor to permeate from at least one side to the other side, and a hydrophobic layer having a hydrophobicity and a hydrophilic layer having a hydrophilic property are stacked. One of the hydrophobic layer or the hydrophilic layer is composed of a PTFE porous membrane formed using PTFE, and the other of the hydrophobic layer or the hydrophilic layer is composed of a breathable sheet having air permeability.

The air permeable sheet is formed using a nonwoven fabric, and the nonwoven fabric preferably has a thickness of 20 µm or more and 1000 µm or less.

It is preferable that the hydrophobic layer and the hydrophilic layer are stacked and configured to contact each other.

1 is a cross-sectional view of a moisture permeable filter medium according to an embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1. In addition, in the following drawings, the same reference numerals are attached to the same or corresponding parts, and the description is not repeated.

As shown in Fig. 1, the moisture permeable filter medium 1 according to the present embodiment has a sheet-like shape. And the moisture permeable filter medium 1 is comprised so that water vapor can permeate|permeate from one side to the other side. Specifically, the moisture permeable filter medium 1 is formed by laminating a hydrophobic layer 2 having hydrophobicity and a hydrophilic layer 3 having hydrophilicity. In addition, hydrophilicity means that the water absorption rate of the material constituting each layer (specifically, the resin itself) is 0.01% or more, and hydrophobicity means that the water absorption rate of the material constituting each layer (specifically, the resin itself) is 0.01%. It says less than. The water absorption is measured under conditions of 23 degrees and 24 hours in accordance with ASTM standard D570.

The moisture permeable filter medium 1 is composed of a porous PTFE membrane formed using PTFE and a breathable sheet having air permeability. Specifically, either one of the hydrophobic layer 2 or the hydrophilic layer 3 is composed of a PTFE porous membrane, and the other of the hydrophobic layer 2 or the hydrophilic layer 3 is composed of a breathable sheet. That is, when the hydrophobic layer 2 is composed of a porous PTFE membrane, the hydrophilic layer 3 is composed of a breathable sheet, and the hydrophilic layer 3 is composed of a porous PTFE membrane, the hydrophobic layer 2 is a breathable sheet It consists of Hereinafter, a case where the hydrophobic layer 2 is composed of a porous PTFE membrane and the hydrophilic layer 3 is composed of a breathable sheet will be described.

When the hydrophobic layer 2 is composed of a porous PTFE membrane, a porous PTFE membrane having hydrophobicity is used. Although it does not specifically limit as the water absorption rate of such a porous PTFE membrane, it is less than 0.01%, and it is preferable that it is 0%. Further, it is preferable that the PTFE porous membrane is porous and has a pressure loss of _{80 mmH 2 O or less at a permeation flow rate of 5.3 cm/sec.} Further, the PTFE porous membrane has a collection efficiency of preferably 60% or more, more preferably 70% or more, and a PF value of 22 or more at a permeation flow rate of 5.3 cm/sec and a measurement particle diameter of 0.1 μm or more and 0.2 μm or less Do. As a method of forming the porous PTFE membrane, the following method can be adopted, for example.

Specifically, a liquid lubricant is added to the PTFE fine powder to form a paste-like mixture. The liquid lubricant is not particularly limited, and any one capable of imparting suitable wettability to the surface of the mixture is particularly preferable as long as it can be removed by extraction treatment or heat treatment. For example, hydrocarbons such as liquid paraffin, naphtha, and white oil are used as liquid lubricants. The amount of the liquid lubricant to be added is not particularly limited, and for example, it is preferably 5 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the PTFE fine powder.

Then, the mixture is preformed, and a preform is formed. It is preferable that the preforming is performed at a pressure such that the liquid lubricant is not separated from the mixture. Next, the obtained green body is formed into a sheet shape by extrusion molding or rolling molding. Thereafter, the obtained molded body is uniaxially stretched or biaxially stretched to make it porous to obtain a PTFE porous membrane. Further, the stretching conditions are not particularly limited, and for example, in a temperature environment of 30° C. or more and 400° C. or less, the stretching ratio is preferably 1.5 times or more and 200 times or less of each axis. In addition, in the case where the firing treatment is not performed in the stretching step, it is preferable to fire the PTFE porous membrane at a temperature equal to or higher than the melting point after the stretching step.

When the hydrophilic layer 3 is composed of a breathable sheet, a breathable sheet having hydrophilicity is used. The water absorption rate of the material constituting the breathable sheet (specifically, the resin itself) is not particularly limited, but it is 0.01% or more, preferably 0.03% or more and 2% or less, and more preferably 0.3% or more and 1.6% or less. It does not specifically limit as a breathable sheet|seat, For example, although a nonwoven fabric, a woven fabric, a mesh, etc. can be used, it is especially preferable to use a nonwoven fabric.

In addition, in the case of thermal welding (thermal lamination) between the PTFE porous membrane (hydrophobic layer 2) and the breathable sheet (hydrophilic layer 3), it is preferable to use a nonwoven fabric containing a thermoplastic material as the breathable sheet. . For example, it is preferable to use a nonwoven fabric composed of synthetic fibers such as polyolefin (polyethylene, polypropylene, etc.), polyamide, polyester, aromatic polyamide, acrylic, polyimide, and composite materials thereof as the breathable sheet.

In addition, as the nonwoven fabric, it is preferable as long as it contains fibers made of two components having a difference in melting point as a raw material. For example, it is possible to use a nonwoven fabric in which the core portion and the outer skin portion are formed of core sheath fibers composed of components having different melting points. As a nonwoven fabric (breathable sheet) made of core sheath fibers, for example, a nonwoven fabric containing core sheath fibers having a core portion made of polypropylene (PP) and an outer skin portion made of polyethylene (PE) may be mentioned. In addition, in such a nonwoven fabric, by PMMA treatment, the PE forming the outer skin portion has hydrophilicity. Alternatively, there may be mentioned a nonwoven fabric including core sheath fibers having a core portion formed of polypropylene terephthalate (PET) and an outer skin portion formed of nylon 6 (PA6). And, such a nonwoven fabric has hydrophilicity by having a hydrophilicity of PA6 forming the outer skin portion. In other words, the hydrophilicity of the nonwoven fabric (breathable sheet) is derived from the configuration of the outer skin portion.

Further, the fibers constituting the nonwoven fabric may be composed of one component, or may be composed of, for example, ethylene vinyl acetate (EVA) fibers. Such a nonwoven fabric has hydrophilicity because EVA is a material having hydrophilicity. Further, the hydrophilicity of the breathable sheet may be configured to have hydrophilicity by plasma treatment of the material constituting the breathable sheet.

When the breathable sheet is a non-woven fabric, the non-woven fabric is not particularly limited as a thickness (that is, the thickness of the hydrophilic layer 3), for example, preferably 20 µm or more and 1000 µm or less, and 50 µm or more and 500 µm or less. It is more preferable. Further, the weight per unit area of the nonwoven fabric is preferably 2 g/m 2 or more and 200 g/m 2 or less, and more preferably 10 g/m 2 or more and 100 g/m 2 or less.

The method of forming the moisture permeable filter medium 1 by laminating the hydrophobic layer 2 and the hydrophilic layer 3 is not particularly limited, and for example, a breathable sheet (preferably, a nonwoven fabric) is heated to soften the PTFE porous material. A method of laminating the hydrophobic layer 2 and the hydrophilic layer 3 can be adopted by pressing (ie, thermal lamination) with the film. Alternatively, a method of laminating the hydrophobic layer (2) and the hydrophilic layer (3) by placing a hot melt or pressure-sensitive adhesive between the porous PTFE membrane and the breathable sheet and pressing the porous PTFE membrane and the breathable sheet is adopted. can do. That is, in the moisture-permeable filter medium 1 of the present embodiment, the hydrophobic layer 2 and the hydrophilic layer 3 are stacked and brought into contact with each other.

The method of compressing the porous PTFE membrane and the air permeable sheet is not particularly limited, and for example, the porous PTFE membrane and the air permeable sheet are laminated and conveyed between a pair of roller members (not shown). A method of continuously pressing the breathable sheet can be employed. Alternatively, a method in which a sheet-shaped porous PTFE membrane and an air permeable sheet are stacked between a pair of plates (not shown) may be disposed and intermittently compressed for each sheet.

The thickness of the moisture-permeable filter medium 1 formed as described above is not particularly limited, and for example, it is preferably 0.02 mm or more and 0.5 mm or less, and more preferably 0.07 mm or more and 0.3 mm or less. Further, the moisture permeability of the moisture permeable filter medium 1 is not particularly limited, and for example, it is preferably 150 g/m 2 or more and 175 g/m 2 or less per hour, and more preferably 160 g/m 2 or more and 170 g/m 2 or less. In addition, the moisture permeability is measured by the method described in the following Examples.

As described above, according to the moisture permeable filter medium according to the present invention, even in a state in which the breathable sheet is laminated on the PTFE porous membrane, it is possible to suppress a decrease in moisture permeability relative to the moisture permeability of the PTFE porous membrane itself.

That is, when two gases having different humidity are disposed adjacent to each other via the moisture permeable filter medium 1, water vapor permeates from one side to the other side of the moisture permeable filter medium 1. At this time, either one of the hydrophobic layer 2 or the hydrophilic layer 3 is composed of a PTFE porous membrane, and the other of the hydrophobic layer 2 or the hydrophilic layer 3 is composed of a breathable sheet, so that the hydrophobic layer ( 2) There is a difference between the amount of water vapor in the hydrophilic layer 3 and the amount of water vapor in the hydrophilic layer 3. And, by this difference in the amount of water vapor, the permeation rate of water vapor from one side of the moisture permeable filter medium 1 to the other side increases. Thereby, the decrease in moisture permeability caused by lamination of the air permeable sheet on the PTFE porous membrane (deterioration in the moisture permeability of the PTFE porous membrane alone) can be suppressed, and a moisture permeable filter medium 1 having good moisture permeability can be obtained.

Specifically, conventionally, when a breathable sheet (non-woven fabric) having the above-described configuration is laminated on a PTFE porous membrane to form a moisture permeable filter material 1, such a moisture permeable filter material 1 has remarkable moisture permeability than the moisture permeability of the PTFE porous membrane alone. Will be degraded. However, as in the present embodiment, while either the hydrophilic layer 3 or the hydrophobic layer 2 is composed of a PTFE porous membrane formed using PTFE, the hydrophilic layer 3 or the hydrophobic layer 2 By using the nonwoven fabric as described above as the breathable sheet constituting the side, it is possible to suppress a decrease in moisture permeability caused by lamination of the breathable sheet on the PTFE porous membrane, and a moisture permeable filter medium 1 having good moisture permeability can be obtained. In particular, it is possible to appropriately suppress a decrease in moisture permeability from the hydrophilic layer 3 side to the hydrophobic layer 2 side (in other words, the water vapor amount in the layer from the high side to the low side).

In addition, since the hydrophobic layer 2 and the hydrophilic layer 3 contact each other, the hydrophilic layer 3 and the hydrophobic layer 2 are more than when another layer is interposed between the hydrophilic layer 3 and the hydrophobic layer 2. ) And the distance becomes closer. For this reason, the movement of water vapor due to the difference in the concentration of water vapor between the hydrophilic layer 3 and the hydrophobic layer 2 is performed more quickly. For this reason, the decrease in moisture permeability caused by lamination of the air permeable sheet on the porous PTFE membrane can be further suppressed, and the moisture permeable filter medium 1 having good moisture permeability can be obtained.

In addition, when two gases having different humidity are disposed adjacent to each other via the moisture permeable filter medium 1, it is preferable to place the gas with the higher humidity on the hydrophilic layer side and the gas with the lower humidity on the hydrophobic layer side. , And vice versa.

In addition, the moisture permeable filter medium according to the present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the present invention. In addition, configurations and methods of the plurality of embodiments described above may be arbitrarily adopted and combined (configuration or method according to one embodiment may be applied to other embodiments, such configurations or methods, etc.), and the following various It goes without saying that a configuration or a method according to the modified example may be arbitrarily selected, and a configuration or a method according to the above-described embodiment may be employed.

For example, in the above embodiment, the hydrophobic layer 2 is formed of a PTFE porous membrane, and the hydrophilic layer 3 is formed of a breathable sheet, but is not limited thereto, for example, hydrophilized PTFE porous membrane. The hydrophilic layer 3 may be formed using the membrane, and the hydrophobic layer 2 may be formed using a breathable sheet having hydrophobicity. As the hydrophilized PTFE porous membrane, for example, a PTFE porous membrane (core sheath structure of PVA and PTFE) subjected to hydrophilization treatment with polyvinyl alcohol (PVA) can be used. On the other hand, examples of the hydrophobic air permeable sheet include those composed of polyethylene (PE) in which the core portion is composed of polypropylene (PP) and the outer shell portion is not hydrophilized.

In addition, in the above embodiment, a moisture permeable filter medium is formed by two layers of the hydrophobic layer 2 and the hydrophilic layer 3, and the hydrophobic layer 2 and the hydrophilic layer 3 are stacked so as to be in contact. In addition, another layer (for example, a nonwoven fabric that does not affect moisture permeability) may be laminated between the hydrophobic layer 2 and the hydrophilic layer 3. In addition, when the hydrophobic layer (2) and the hydrophilic layer (3) are stacked, other layers (e.g., do not affect the moisture permeability) on the surface on the side of the hydrophobic layer (2) or on the surface of the hydrophilic layer (3). Nonwoven fabric, etc.) may be laminated.

Example

Hereinafter, an embodiment of the present invention will be described.

1. Materials used

(1) hydrophilic layer

Hydrophilic PTFE porous membrane (made by treating Nitto Denko's PTFE porous membrane with PVA to make it hydrophilic)

EVOH (ethylene-vinyl alcohol copolymer) filter media (Eval, manufactured by Kurare)

Non-woven fabric 1 (non-woven fabric containing core sheath fibers with a core part of PP and an outer skin part of PE was treated with PMMA) (non-woven fabric: HOP manufactured by Hirose Seishi)

Non-woven fabric 2 (non-woven fabric containing core sheath fibers with a core part of PET and an outer skin part of PA-6) (Colback made by BONAR)

Non-woven fabric 3 (non-woven fabric containing EVA fibers) (manufactured by Nitto Denko)

(2) hydrophobic layer

・PTFE porous membrane (manufactured by Nitto Denko)

Non-woven fabric 4 (non-woven fabric containing core sheath fibers in which the core part is PP and the outer part is PE) (HOP made by Hirose Seishi)

Non-woven fabric 5 (non-woven fabric containing core sheath fibers in which the core part is PET and the outer skin part is PE) (SE100SHO made by Unitika)

In addition, the hydrophilic PTFE porous membrane is formed by the following method. Specifically, 19 parts by weight of a liquid lubricant (dodecane) was uniformly mixed with 100 parts by weight of PTFE fine powder (manufactured by Daikin, Polyflon F104) to form a mixture, and the mixture was preformed. Subsequently, the obtained green body was paste-extruded into a sheet shape to form a sheet-shaped molded body. The obtained sheet-shaped molded article was passed between a pair of metal rolling rolls to obtain a 200 µm-thick long sheet, and then the liquid lubricant was dried and removed. Then, the obtained long sheet was stretched three times in the longitudinal direction at a stretching temperature of 280°C, and further stretched six times in the width direction at a stretching temperature of 150°C by a tenter method to obtain a PTFE porous membrane.

Then, after impregnating the obtained porous PTFE membrane with isopropyl alcohol, it was immersed in a PVA solution. Thereafter, PVA was crosslinked with glutaraldehyde to obtain a hydrophilic PTFE porous membrane.

In addition, the PTFE porous membrane constituting the hydrophobic layer is formed by the following method. Specifically, 19 parts by weight of a liquid lubricant (dodecane) was uniformly mixed with 100 parts by weight of PTFE fine powder (manufactured by Daikin, Polyflon F104) to form a mixture, and the mixture was preformed. Subsequently, the obtained green body was paste-extruded into a sheet shape to form a sheet-shaped molded body. The obtained sheet-shaped molded article was passed between a pair of metal rolling rolls to obtain a 200 µm-thick long sheet, and then the liquid lubricant was dried and removed. Then, the obtained long sheet was stretched 14 times in the longitudinal direction at a stretching temperature of 280°C, and further stretched 30 times in the width direction at a stretching temperature of 150°C by a tenter method to obtain a PTFE porous membrane constituting a hydrophobic layer.

2. Measurement of water absorption

Among the materials used, except for the EVOH filter medium, the water absorption was measured under conditions of 23 degrees and 24 hours in accordance with ASTM standard D570. For the EVOH filter medium, the mass ratio of the filter medium increasing when the EVOH filter medium of a predetermined size was immersed in water was measured as the water absorption.

3. Fabrication of moisture permeable filter media

The moisture permeable filter media of Examples 1 to 4 and the moisture permeable filter media of Comparative Examples 1 to 4 were prepared by laminating each of the materials to be used so as to have the layer structure shown in Table 1 below.

4. Measurement of moisture permeability

A moisture absorbent (calcium chloride) having been weighed was accommodated in a cup (having an opening surface of φ 60 mm in accordance with JIS L 1099), and a moisture-permeable filter medium was installed in the opening of the cup so as to cover the entire opening surface of the cup without a gap. At this time, the distance between the desiccant and the moisture permeable filter medium was 3 mm, and the moisture permeable area was 0.00283 m 2. A cup covered with a moisture permeable filter material with an opening surface was placed in a thermostat with a humidity of 80% and a temperature of 30°C for one hour. Thereafter, such a cup was taken out from the thermostat, and the desiccant was weighed. And, using the mass difference (i.e., the amount of water vapor absorbed by the desiccant) A and the area B of the opening surface of the cup, the moisture permeability was calculated by the following equation (1). About the moisture permeability, it is shown in Table 1 below.

Moisture permeability (g/m²/h)=A/B... (One)

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Comparing each of the examples with each of the comparative examples, it can be seen that the decrease in the moisture permeability is suppressed in each example compared to the moisture permeability of the reference example. That is, a hydrophobic layer and a hydrophilic layer are stacked, one layer is composed of a PTFE porous membrane, and the other layer is composed of a nonwoven fabric, thereby suppressing the decrease in moisture permeability caused by lamination of the nonwoven fabric on the PTFE porous membrane. I can.

Further, in general, the moisture permeability is inversely proportional to the thickness of the moisture permeable filter medium, but when comparing Examples 1 to 3, it is seen that the moisture permeability of Example 2, which has the thickest thickness, is the highest. That is, when the hydrophobic layer is composed of a porous PTFE membrane and the hydrophobic layer is composed of a nonwoven fabric, it is seen that the greater the difference in water absorption between the hydrophobic layer and the hydrophilic layer, the higher the moisture permeability.

One… Moisture permeable filter media, 2... Hydrophobic layer, 3… Hydrophilic layer

Claims (3)

It is formed in a sheet shape and is configured to transmit water vapor from at least one side toward the other side,
It is laminated and configured so that the hydrophobic layer having hydrophobicity and the hydrophilic layer having hydrophilicity are in contact,
One of the hydrophobic layer or the hydrophilic layer is composed of a PTFE porous membrane formed using PTFE, and the other of the hydrophobic layer or the hydrophilic layer is composed of a breathable sheet having air permeability,
The hydrophilic layer has an absorption rate of 0.01% or more, and the hydrophobic layer has an absorption rate of less than 0.01%. The method according to claim 1, wherein the breathable sheet is formed using a nonwoven fabric,
The nonwoven fabric is a moisture-permeable filter medium having a thickness of 20 µm or more and 1000 µm or less. delete

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